It is generally known for a cellular wireless communication device (WCD) to engage in voice calls via a cellular radio access network (RAN). A traditional RAN includes one or more mobile switching centers (MSCs), each of which is connected with one or more base station controllers (BSCs), and each BSC is in turn connected with one or more base transceiver stations (BTSs) that define cellular wireless coverage areas in which wireless communication devices can operate.
Typically, each BTS includes an antenna tower with antennas arranged to radiate in a desired pattern so as to produce a desired level of coverage, defining a cell and a number of cell sectors. Each BSC then functions to manage air interface communications, such as to assign air interface traffic channels over which WCDs can communicate, and to manage handoff of communications as a WCD moves between coverage areas (e.g., sectors). Each MSC, in turn, functions as a switching point, to provide connectivity between various WCDs in its coverage, and between WCDs and the public switched telephone network, and further to facilitate handoff of communications as a WCD moves between BSC serving areas or MSC serving areas.
Conventionally, each WCD has an assigned identifier, such as a mobile identification number (MIN) or mobile directory number (MDN), and each WCD has a service profile stored in a home location register (HLR). Each MSC is in turn coupled with the HLR, typically by an out of band signaling network such as a Signaling System #7 (SS7) network for instance.
When a WCD powers on in, or otherwise enters, a coverage area (such as an area served by a particular BTS, BSC, or MSC), the WCD will register with the radio network infrastructure, so the system can know where the WCD is located (e.g., for purposes of directing calls to the WCD) and so the system can verify that the WCD is authorized to engage in wireless communications. In a typical radio network registration process, the WCD sends a radio access registration message over the air to the RAN and, assuming successful registration, then receives a radio access registration response message from the RAN. Further, during a typical radio network registration process, the HLR will deliver a copy of the WCD's service profile to the serving MSC, so that the MSC can then reference the profile when serving the WCD.
In a system compliant with the well known CDMA (e.g., CDMA2000) and IS-41 protocols, for example, a WCD engages in radio network registration by sending over the air (in an air interface access channel) to the BTS and, in turn to the BSC, an “access probe,” which carries an identifier of the mobile station and other pertinent information. When the BSC receives the access probe, the BSC passes the access probe along to the MSC, and the MSC then sends an IS-41 “Registration Notification” (REGNOT) message to the HLR. The HLR in turn updates the WCD's profile to indicate where the WCD is operating (e.g., which MSC is serving the WCD) and may further carry out an authentication process, and the HLR then sends an IS-41 registration notification return result (regnot_rr), typically including the WCD's service profile, to the MSC. The MSC then sends a registration acknowledgement over the air (in an air interface paging channel) to the WCD to complete the registration process.
Once the WCD is registered with the RAN, the WCD can then place and receive voice calls (assuming the WCD's service profile and configuration allow it). To place a call, for instance, the WCD may send a call origination message over the air (in an air interface access channel) to the RAN, providing a set of dialed digits indicative of a called party phone number. Upon receipt of the call origination message, the MSC may then direct the BSC to assign an air interface traffic channel for use by the WCD, and the MSC may further engage in call setup signaling (e.g., ISDN User Part (ISUP) signaling) to set up the call with a remote switch serving the called party. When the called party answers, the MSC may then connect the call through to the WCD. Similarly, when the MSC receives a request to connect an incoming call to the WCD, the MSC may page and alert the WCD over the air (in an air interface paging channel). When the WCD answers the call, the MSC may then connect the call through to the WCD.
One of the important features of many RAN systems is the ability to manage WCD mobility, such as handoff of calls from one coverage area to another as a WCD moves between coverage areas. As noted above, a BSC typically serves this function for handoffs between coverage areas (e.g., sectors) that the BSC serves. For handoffs between BSCs, on the other hand, IS-41 defines a process in which the BSC that first handles the call (the “anchor” BSC) remains in the call path, and bearer traffic is shunted between that anchor BSC and the BSC currently serving the WCD, so as to maintain connectivity as the WCD moves between BSC coverage areas.
It is also generally known today for WCDs to be able to engage in wireless packet data communication. In a system compliant with the well known CDMA2000® protocol, for instance, a WCD (such as a cell phone, wirelessly equipped PDA, or wirelessly-equipped computer) can obtain packet data connectivity by signaling with the RAN and by signaling through the RAN with a packet data serving node (PDSN) that sits as a gateway on a packet-switched network.
In particular, after the WCD enters a wireless coverage area and successfully engages in radio network registration, the WCD can send a packet-data origination message via an air interface access channel to the RAN. Under CDMA2000®, the packet-data origination message may be largely the same as a traditional call origination message, except that it would include a special service option code that signifies a request to establish packet-data connectivity. Upon receipt of the packet-data origination message, a BSC or other radio network controller (RNC) in the RAN may then assign an air interface traffic channel for use by the WCD as a radio link, and the RAN may signal to a PDSN to trigger establishment of a data link, such as a point-to-point protocol session (i.e., a serialized packet-data connection), between the PDSN and the WCD. Once that data link is established, the WCD may then send a mobile-IP registration request to the PDSN, which the PDSN may forward to a mobile-IP home agent, and the home agent may then assign an IP address for use by the WCD to engage in communications on the packet-switched network.
It is further known for WCDs to be able to engage in voice-over-IP (VoIP) and other packet-based real-time media communications. For example, after a WCD gains radio access and then packet data connectivity as described above, the WCD may engage in call setup signaling, such as Session Initiation Protocol (SIP) signaling or H.323 signaling for instance, to set up a packet-based real-time media session with another entity on the packet-switched network. Such a session could carry media according to the well known Real-time Transport Protocol (RTP), as described in RFC 1889, or in some other manner.
When a WCD engages in wireless packet data communications, and particularly packet-based real-time media communications such as VoIP, an additional mobility management issue arises. In particular, as a WCD moves between PDSN serving systems, the WCD must establish connectivity with the new PDSN, and the mobile-IP home agent must be informed that the new PDSN is serving the WCD. In some cases, this process of handing off to a new PDSN can take on the order of 6 seconds to complete, which may unfortunately disrupt real-time media communications.